Vitamin D intake has been associated with breast density reduction in premenopausal women.

Supplementation with vitamin D3 in premenopausal women may not have a significant effect in decreasing breast density percentage, according to a study published in Cancer Epidemiology, Biomarkers, and Prevention.

Increased breast cancer risk has been correlated with high breast density, which indicates how much stromal and epithelial tissue is in the breast. Prior studies have shown that vitamin D intake may be associated with breast density reduction for premenopausal women.

This double blind, placebo-controlled trial randomized 405 premenopausal women with no prior history of cancer 1:1:1:1 to receive placebo or vitamin D3 in strengths of 1000, 2000, or 3000 IU/day. Study participants received a mammogram at baseline and at the 1-year follow-up. The primary outcome of the study was the mean change in percent mammographic breast density.

The mean ± SE change in breast density for patients randomized to receive vitamin D3 1000 IU/day was –5.5% ± 0.5%, and vitamin D3 2000 IU/day was –5.9 ± 0.5%. The changes were not significant in comparison to the reduction seen in the placebo arm (–5.7 ± 0.5%; P =1.0). Women receiving vitamin D3 3000 IU/day had a slight decrease in breast density, but less than that of placebo (–3.8 ± 0.5%; P =.03).

The study results show that while premenopausal women receiving vitamin D3 supplementation may experience a decrease in breast density, the observed benefit is no greater than that of placebo in reducing breast cancer risk.